Var :


1. The var is the oldest keyword to declare a variable in JavaScrip. The scope of the var keyword is the global.
2. In the var tab, when you will run the code, you will see an error as a is not defined because var variables are only accessible in the function scope.

Let:


1.The let keyword is an improved version of the var keyword.The scope of a let variable is only block scoped.
2. In the let tab, when you run the code, you will see an error as i is not defined because let variables are only accessible within the block they are declared.

Const :


1. The const keyword has all the properties that are the same as the let keyword, except the user cannot update it.

Regular Functions :

1. The regular functions are the usual way to define methods on classes.
2. As seen in the previous section, the regular function can easily construct objects.

Arrow Functions :

1. The behavior of this inside of an arrow function differs considerably from the regular function's this behavior. The arrow function doesn't define its own execution context.
2. You can return values from the arrow function the same way as from a regular function, but with one useful exception.

The main difference between map and forEach is that the map method returns a new array by applying the callback function on each element of an array, while the forEach method doesn't return anything.
. map() goes through all entries then creates a new array using the function supplied.
. find() locates a specific entry by a predicate and returns it.